Handheld electronic devices such as smartphones, tablets, and smartwatches are popular with consumers and are sold in great numbers. The majority of these devices employ a touch sensitive display for both display of output to a user and accepting data as input from a user. Most of these touch sensitive displays utilize capacitive touch sensing.
A typical such touch sensitive display includes a display layer constructed from technology such as LCD, IPS, or AMOLED, as well as a sensing layer. A typical sensing layer includes a plurality of parallel drive lines, and a plurality of parallel sensing lines. The sensing lines capacitively intersect the drive lines. In operation, a single drive line is driven with a wave, such as a square wave or sine wave. The capacitance between the sensing lines and the driven drive line is sensed at the point where they intersect. Presence of a human finger or a conductive object alters the expected capacitance at the intersection point, and by measuring the change in capacitance, a touch between the finger or object and the touch sensitive display can be detected.
These touch sensitive displays include a touch screen controller. The touch screen controller includes a separate receiver coupled to each sense line to measure the capacitance thereof. The capacitances of the sense lines can be used by processing circuitry, such as a system on chip of the electronic device, to determine contact points between human fingers and the touch sensitive display. These contact points are used as input.
Since the above described handheld electronic devices are powered by batteries, it is desirable for the life of those batteries to be as long as possible. Therefore, reducing the amount of power consumed by various components of electronic devices is commercially desirable and a technical challenge.
The above described touch screen controllers provide robust performance, but may consume more power than desired. Therefore, new designs for touch screen controllers that consume less power are desirable.